MDL-65292 style: Fix all function declarations white space

This has been generated running the following Sniffs, all
them part of the Moodle's CodeSniffer standard:
- PSR12.Functions.ReturnTypeDeclaration
- PSR12.Functions.NullableTypeDeclaration
- moodle.Methods.MethodDeclarationSpacing
- Squiz.Whitespace.ScopeKeywordSpacing

All them are, exclusively, about correct spacing, so the changes
are, all them, only white space changes.

Only exceptions to the above are 3 changes what were setting the
return type in a new line, and, when that happens, the closing
parenthesis (bracket) has to go to the same line than the colon.

lib/testing/generator/data_generator.php

@@ -1326,7 +1326,7 @@ EOD;
      * @param   array $data Array with data['name'] of category
      * @return  \core_customfield\category_controller   The created category
      */
-    public function create_custom_field_category($data) : \core_customfield\category_controller {
+    public function create_custom_field_category($data): \core_customfield\category_controller {
         return $this->get_plugin_generator('core_customfield')->create_category($data);
     }
 
@@ -1336,7 +1336,7 @@ EOD;
      * @param   array $data Array with 'name', 'shortname' and 'type' of the field
      * @return  \core_customfield\field_controller   The created field
      */
-    public function create_custom_field($data) : \core_customfield\field_controller {
+    public function create_custom_field($data): \core_customfield\field_controller {
         global $DB;
         if (empty($data['categoryid']) && !empty($data['category'])) {
             $data['categoryid'] = $DB->get_field('customfield_category', 'id', ['name' => $data['category']]);